Understanding factors that influence drug withdrawal in men and women is an essential component of successful drug abuse treatment. This within-subjects study will explore the time course of tobacco withdrawal in men and women over a 5-day period using a placebo control design. Smokers will participate in three, 5-day conditions separated by a minimum 48-hour washout period. Conditions will span Monday-Friday and subjects will attend the research facility for about one hour on each weekday for periodic monitoring on various measures (e.g., subjective, physiological, behavioral, compliance). Weekends will serve as washout periods during which subjects will smoke their usual brand of cigarettes. Conditions vary by the cigarettes to be smoked: in one condition subjects will smoke denicotinized cigarettes, in another they will smoke control (nicotinized) cigarettes, and in the third they will abstain from smoking. Smoking conditions will be double-blind and all these conditions will be ordered by Latin Square. Each condition will include periodic monitoring of subjective symptoms of tobacco withdrawal, performance measures, levels of urinary cotinine (a nicotine metabolite), expired air carbon monoxide (CO), and several physiological variables. Subjective and performance measures will be administered daily, Monday-Friday. Monitoring levels of urinary cotinine and expired CO will be done thrice weekly (i.e., Monday, Wednesday, and Friday) and will be used to assess compliance with smoking restrictions. Additionally, compliance with smoking restrictions will be reinforced monetarily twice weekly (i.e., Wednesday and Friday). Results from this study will help to determine: a) the extent to which cigarette smokers are physically dependent on nicotine, the long-term contribution of non-nicotine, tobacco-related factors in the withdrawal suppression produced by denicotinized cigarettes, and c) whether men and women differ in their response to the nicotine/tobacco withdrawal syndrome.